A conventional laundry treatment apparatus includes a cabinet defining the external appearance of the laundry treatment apparatus, a tub installed inside the cabinet, a drum rotatably installed inside the tub, the drum serving to wash laundry, a power transmission unit installed to transmit torque to the drum in order to rotate the drum, and a motor fixed to the power transmission unit, the motor having a rotating shaft installed to penetrate the tub.
The drum may fail to maintain dynamic balance due to the position of the laundry contained in the drum, thus being rotated.
Dynamic balance means the state in which centrifugal force or a moment made by the centrifugal force when a rotator rotates becomes zero with respect to a rotation axis. In the case of a rigid body, dynamic balance is maintained when the distribution of the mass is constant about a rotation axis.
Accordingly, the dynamic balance of the laundry treatment apparatus may be understood as the case where, when the drum, in which laundry is stored, rotates, the distribution of the mass of the laundry is within an allowable range about the rotation axis of the drum (i.e. the case where the drum rotates while vibrating within an allowable range).
On the other hand, in the laundry treatment apparatus, the state in which dynamic balance is broken (i.e. the unbalanced state) is the state in which the distribution of the mass of the laundry is not constant about the rotation axis of the drum while the drum is rotating. This occurs when the laundry is not uniformly distributed inside the drum.
When the drum rotates in the unbalanced state, the drum vibrates, and the vibrations of the drum are transmitted to the tub or the cabinet, causing noise.
The conventional laundry treatment apparatus includes a balancing unit for eliminating the unbalance of the drum. A ball balancer or fluid balancer in which a ball or fluid is provided inside a housing, which is fixed to the drum, has been used as the balancing unit of the conventional laundry treatment apparatus.
The ball balancer or fluid balancer included in the conventional laundry treatment apparatus is configured to control unbalance caused by laundry by the movement of the ball or fluid in the direction opposite the direction in which the laundry that is causing the unbalance is located, when the rotational path of the drum fluctuates due to the laundry.
However, the control of unbalance described above is available in a steady state in which the vibrations of the drum are within a given range, but cannot anticipate great effects in the transient vibration state in which the vibrations of the drum are excessive.
In addition, the conventional balancing unit has difficulty in rapidly (actively) eliminating the unbalance once the unbalance has occurred.
In addition, although there is a method of rapidly supplying water to the balancer in order to rapidly eliminate the unbalance, this method has difficulty in efficiently draining the water supplied to the balancer.
In addition, the method of supplying water to the balancer in order to eliminate the unbalance requires the balancer to be mounted to the drum. In this case, however, a space is formed between the balancer and the drum, which makes it difficult to efficiently supply water to the balancer.